1. Technical Field
This disclosure is generally related to an encoder and in particular to a digital encoder. This disclosure describes a circuit that can convert a conventional digital signal into a time encoded pulse signal. The output pulse signal has only two amplitude levels. The transition times of the output pulse are not aligned to a clock, but rather convey encoded information.
2. Description of Related Art
A typical single time encoder circuit includes a limit cycle oscillator. Such a single time encoder circuit can perform analog to pulse time encoded conversion. However, such a circuit is incapable of digital to pulse conversion. See A. Lazar and L Toth, “Perfect Recovery and Sensitivity Analysis of Time Encoded Bandlimited Signals,” IEEE Trans. on Circuits and Systems-I, vol. 51, no. 10, pp. 2060-2073, October 2004.
In the prior art, there is no circuit for directly converting a digital signal into a pulse time encoded signal. The conversion from digital to pulse could have been done by doing first a conversion from the digital domain to the analog domain and then using a conventional time encoder to convert the analog domain signal into the pulse domain. FIG. 1 shows such a prior art analog to pulse domain time encoder. However, in such an approach the conventional time encoder requires an analog amplifier. The analog amplifier limits linearity and introduces noise. The new digital domain to pulse domain encoder disclosed herein eliminates the need for any linearity-limiting analog amplifier. The new circuit is also simpler as it does not require an addition operation before the integrator of the time encoder.
FIG. 1 is a block diagram of a prior art analog domain to pulse domain time encoder 100 which is known in the art. The time encoder 100 is responsive to an analog input signal 102 and generates a time encoded output signal 114. The analog input signal 102 is connected to an amplifier 104, the amplifier 104 is connected to an adder 106, the adder 106 is connected to an integrator 108, and the integrator 108 is connected to a quantizer 110, typically a hysteresis quantizer. A portion of an output of the quantizer 110 is fed back via an amplifier 112 to the adder 106. The time encoded output signal 114 is available at the output of the quantizer 110. The time encoder 100 encodes the analog input signal 102 into the time encoded output signal 114. If the analog input signal 102 is bandlimited, the analog input signal 102 can be encoded substantially without loss of information. That is, the analog input signal 102 can be recovered from a timing of the time encoded output signal 114. A time decoding machine can be used to recover the analog input signal 102 from the time encoded output signal 114. Assuming ideal elements no quantization error is introduced by this encoder 100.
A typical power analog amplifier, having an analog input and an analog output, includes a delta sigma modulator, an amplifier and a band-pass filter. This circuit provides high power amplification. However, such a circuit is incapable of time encoding without introducing additional quantization error. A delta sigma modulator in the power analog amplifier converts an analog input signal into pulses aligned to a clock introducing a quantization error. Furthermore, the power analog amplifier processes only an analog input, and not a digital input. See M. Iwamoto, A. Jayaraman, G. Hannington, P. Chen, A. Bellora, W. Thornton, L. Larson and P. Asbeck, “Bandpass Delta-Sigma Class-S Amplifier” Electronic Letters, vol. 36, no. 12, June 2000, pp. 1010-1012.